Aqueous trifluorethanol solutions simulate the environment of DNA in the crystalline state

We took 28 fragments of DNA whose crystal structures were known and used CD spectroscopy to search for conditions stabilising the crystal structures i n solution, All 28 fragments switched into their crystal structures in 60-8 0% aqueous trifluorethanol (TFE) to indicate that the crystals affected the conformation of DNA like the concentrated TFE. The fragments crystallising in the B-form also underwent cooperative TFE-induced changes that took pla ce within the wide family of B-form structures, suggesting that the aqueous and crystal B-forms differed as well. Spermine and magnesium or calcium ca tions, which were contained in the crystallisation buffers, promoted or sup pressed the TFE-induced changes of several fragments to indicate that the c rystallisation agents can decide which of the possible structures is adopte d by the DNA fragment in the crystal.